1. Field of the Invention
This invention relates to a picture image discriminating apparatus for discriminating the classification of a picture image of document, i.e. a linear picture with a linear picture image as principal constituent, a tonal picture having a tone, or a hybrid picture for which the linear picture and the tonal picture are mixed by means of a picture image density information obtainable through scanning the picture image of document.
2. Description of the Prior Art
A copying technique has been so improved of late that a copy of satisfactory picture quality is obtainable from a document consisting only of a linear picture or a tonal picture. Namely, a decision of the linear picture and tonal picture is made by visual observation, an operating button to specify processing conditions for the linear picture or tonal picture is prepared independently, an operator will select a suitable operating button as the result of visual observation, thereby obtaining a copy. Therefore, there may be a case where an erroneous decision or operation leads to a wasteful copying.
Further, the situation is such that a copy will have to be obtained as fast as possible and also as efficiently as possible, and a copying machine provided with an automatic document feed motion (ADF) has rapidly been prevailing today, therefore the above-mentioned picture image discriminating operation by visual observation is not to cope with the object referred to as above, and such operation cannot be applied practically on the copying machine provided particularly with ADF motion.
On the other hand, when a picture image data is compressed to transmission or store like facsimile and picture image data base, information compression efficiency is not secured unless a coding suitable for each linear picture and tonal picture is applied, and hence a picture image discriminating apparatus superior in performance has been required.
There is given hitherto a picture image discriminating method (patent application Ser. No. 120623/1980) which comprises the steps of scanning a document, forming a histogram according to a density distribution of each spot of the document, and thus discriminating picture images from a pattern of the histogram, however, while effective chiefly to a linear picture information, it involves a hardship for application on a tonal picture.
Namely, a unit reading size (scanning spot) for the image discrimination is very small as in the case of picture image pickup, therefore the method is superior to pickup dimension and tone of the line for linear picture, however, tone of a detail and dot or stain of a meshy picture are picked up for a tonal picture, which may lead sometimes to an erroneous discrimination, and the method is next to incompetent for a hybrid picture.